query: mock + libselinux-mock.so LD_PRELOAD... why?

[Paul Howarth]

Michael E Brown wrote:
>     I need a little bit of help understanding what the
> 'libselinux-mock.so' LD_PRELOAD was supposed to be doing. I released and
> pushed out mock-0.8 without this. I have rebuilt most of rawhide with
> this new mock version and have not seen anything that I directly can say
> was a failure due to this being missing, so I am sort of not seeing the
> point.
> 
>     I have searched around as much as I can to try to understand why
> this was put into place. From what I can understand, it was only put in
> in the FC2 timeframe to fix some problems with the selinux policy on the
> host machine. These *appear* to have been fixed in the host selinux
> policy, so again, i dont see a reason to keep this around.
> 
>     Jesse mentioned on IRC, though, that this might be needed, so I pose
> this question. I've a local branch set up with the 0.8.x code and the
> LD_PRELOAD put back in. So, I can quickly spin a new release with this
> back in if it is actually needed. So far, I havent convinced myself it
> is needed, though...
> 
>     Could somebody please enlighten me?

I suspect it was there to convince rpm that selinux was disabled and 
hence prevent it from trying to set the contexts of installed files. If 
rpm doesn't set the context, the files are installed as mock_var_lib_t 
(assuming my policy module from the wiki is loaded), and this is a 
"neutral" type that doesn't cause any problems. However, if rpm sets the 
contexts of files it installs, it'll set things like /sbin/ldconfig to 
ldconfig_exec_t, and there is now a transition defined in policy from 
unconfined_t to ldconfig_exec_t. The result of this is that some 
processes such as ldconfig get run "confined" in the chroot and fail as 
a result because not *all* file contexts are set up as they would be on 
the host system, which is what the policy is set up for.

I've not quite figured out all te ins and outs of it but a tell-tale 
sign of there being a problem is to look (ls -lZ) at the root 
directories of your chroots and see if they look like this:

/var/lib/mock/fedora-2-i386-core/root:
drwxr-xr-x  root root system_u:object_r:bin_t:s0       bin
drwxr-xr-x  root root system_u:object_r:boot_t:s0      boot
drwx------  root mock system_u:object_r:mock_var_lib_t:s0 builddir
drwxrwsr-x  root mock system_u:object_r:mock_var_lib_t:s0 dev
drwxr-xr-x  root root system_u:object_r:etc_t:s0       etc
drwxr-xr-x  root root system_u:object_r:home_root_t:s0 home
drwxr-xr-x  root root system_u:object_r:root_t:s0      initrd
drwxr-xr-x  root root system_u:object_r:lib_t:s0       lib
drwxr-xr-x  root root system_u:object_r:mnt_t:s0       mnt
drwxr-xr-x  root root system_u:object_r:usr_t:s0       opt
drwxrwsr-x  root mock system_u:object_r:mock_var_lib_t:s0 proc
drwxr-x---  root root system_u:object_r:user_home_dir_t:s0 root
drwxr-xr-x  root root system_u:object_r:bin_t:s0       sbin
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 selinux
drwxrwsr-x  root mock system_u:object_r:mock_var_lib_t:s0 sys
drwxrwxrwt  root root system_u:object_r:tmp_t:s0       tmp
drwxr-xr-x  root root system_u:object_r:usr_t:s0       usr
drwxr-xr-x  root root system_u:object_r:var_t:s0       var

rather than this:
/var/lib/mock/fedora-3-i386-core/root:
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 bin
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 boot
drwx------  paul mock system_u:object_r:mock_var_lib_t:s0 builddir
drwxrwsr-x  root mock system_u:object_r:mock_var_lib_t:s0 dev
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 etc
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 home
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 initrd
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 lib
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 media
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 mnt
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 opt
drwxrwsr-x  root mock system_u:object_r:mock_var_lib_t:s0 proc
drwxr-x---  root root system_u:object_r:mock_var_lib_t:s0 root
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 sbin
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 selinux
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 srv
drwxrwsr-x  root mock system_u:object_r:mock_var_lib_t:s0 sys
drwxrwxrwt  root root system_u:object_r:mock_var_lib_t:s0 tmp
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 usr
drwxr-xr-x  root root system_u:object_r:mock_var_lib_t:s0 var

(it's best to remove any cache or existing root and generate a fresh one)

I'd like to try a version with the LD_PRELOAD back in if possible.

Paul.